Heat transfer and refrigeration



Jara. il, 1938. T. MIDGLEY, JR.. ET AL 2,104,882

- HEAT TRANSFER AND REFRIGERATION Original Filed NOV. 19, 193] 6 CCL3 0'0 e@ 2 INVENTORS 7= cHcLF Y Thoma.: Mid /e '.e,

9 .y J Alberi' L. Henne, and

ZF Z BY Pobcfr R New ATTORNEYS Patented Jan. li, 1938 treoA TESv l'HEAT TRANSFER AND REFRIGERATION Thomas Midgley, Jr., Worthington, Albert L.

Henne, Columbus, and Robert R. McNary, Dayton, Ohio,'assignors to General Motors Corporation, Dayton, Ohio, a corporation of Delaoriginal application November-:19, 1931, serial Divided and this application May 1, 1934,' Serial N0. 723,372

s claims.

This application relates to the art of transferring heat from one point to another and specifcally to the art of refrigeration and is a' division of application Serial Number 516,052, patented July 31, 1934, No. 1,968,049. A p

Heretofore, as far as we are aware, refrigerants and heat transfer agents have been chosen chiefly for their boiling points and stability in the refrigerati'ng or heat transfer cycle irrespective of other desirableproperties, such as non-infiammability and non-toxicity.

It is the object of our invention, on the other hand', to provide a process of refrigeration and, generically, a process of heat transfer in which these desirable properties, such as 'non-innammability and non-toxicity, are obtained in combination with the desired boiling points.

Broadly stated, the part of our processwhich deals with the controllingof the properties of the refrigerating or heat transfer agents consists in replacing hydrogen by iluorine or otherhalogen, or both, in aliphatic hydrocarbons in which at least one hydrogen has already been replaced by fluorine.

Broadly stated, the part of our process which relates to the` transfer of heat or the production of refrigeration comprises changing. the physical Y state of, for example, by condensing or evaporating, a halo-iiuoro derivative of an aliphatic hydrocarbon, and dissipating to, or withdrawing from, an object to be heated or cooled, thelatent heat necessary for changing the physical state of the said derivative. By a halo-nuoro derivative of an aliphatic hydrocarbon we mean aderivative containing more than one uorlne atom with or without other halogen atoms, or one uorine atom with one or more other halogen atoms.

Referring now specically to oui mode of con-4 trolling the properties of the refrigerating or heat .transfer agent, aliphatic monouorides form the structural nucleus on which the agents are built. Broadly speaking, if in the structural formula CHSF we increase the uorine content (number of atoms) by the substitution of fluorine for hydroation in limitations imposed.

(Cyl. l62---178) Because there are several variables, and because of the value of relative proportions, we have placed the compounds of the group just discussed on plots wherein I V Fig. l is a plot applying the rules of substitution to typical groups having one carbon atom,

Fig. 2 is a plot applying the rules to groups having two carbon atoms, and

Fig. 3 is a key to Fig. 2, showing the radicals corresponding to the numbers used in Fig. 2.'

Referring to the plots generally, the dashed lines indicate fluorine substitutions and the solid lines indicate chlorine substitution. SimilarV plots are obtained with bromine and iodine in place of chlorine except that the plot is elongated in the direction of higher temperatures with bromine, while with iodine the temperatures are still more elevated. The amount of elongation is readily determined by applying the boiling points of some of these compounds.

Referring specically to Fig. y1, this plot contains all the compounds which can be derived from CHaF by chlorine and/or fluorie substitutions, together with data which assist in the formation of the plot. On the base line appear the. numerals zero to` four which show halogen Vcontent, and the vertical line gives the approximate boiling points in degrees centigrade. At each point of intersection is given the chlorine and iiuorlne content and the complete formula of the corresponding compound is found by making this halogen substitution for hydrogen in the formula CH4. We have drawn a horizontal dashed line at about 25 centigrade to indicate approximately the optimum vapor pressure conditions which we desire for operating an air cooled refrigerator. It is obvious that one may deviate more or less from this line to obtain optimum conditions which include someA other factors, so that within the neighborhood of this line we can provide a suitable refrigerant to meet a wide vari- If under other refrigerating conditions another optimum line is found desirable, the same choice may be made'in the neighborhood of that line. In fact, the actual operation of the refrigerator and the providing of the characteristics of the refrigerant are here combined as one problem so as to obtain the most desirable process of refrigeration under a given set of conditions. I

In Fig. 2 we have shown the same mode of controlling the properties of a refrigerant carried to compounds of the same type as in Fig. 1 but having two carbon atoms.A The key to the chart is given in Fig. 3. For example, compound 0.1 is

CH3.CH2F, compound 2.9 is CHFaCCl-ZF, compound 1.5 is CHzFCI-IClz, and compound 2.2 is CHFz.CHFz.

When We choose as our nucleus a compound having'two or more carbon atoms We find that the structural formula gives a choice as to Where the substitutions of the halogens shall be made. For example, the structural formula of C2H5F is CHsCHzF, which has a boiling point at about 32 C. If we make a fiuorine substitution for hydrogen in the second radical of this structural formula so that it reads GHz-CHFz we have a refrigerating agent whose boiling point is about 26 C. If we make the fluorine substitution for hydrogen onto the other carbon atom so that the formula reads CHzF- CHzF the boiling point of this refrigerant is about 5 C. Thus the rst type of substitution yields a compound boiling substantially lower than the compound obtained by the second type of substitution and the chart shows this to be general. The substitution of chlorine, bromine or iodine for hydrogen raises the boiling point, but the substitution in a radical which does not already contain a halogen raises the boiling point more than when the substitu tion is made in a radical which already contains a halogen. I v

The plot may be expanded in like manner with other aliphatic mono-iluorides. As the number of carbon atoms increases the complexity and extent of the plot will increase together with the number of halogens present. These halogen derivatives of aliphatic mono-fluorides may be represented b-y the formula C represents carbon and n the number of carbon atoms in the molecule which is always equal to one or more.

H represents hydrogen and m the number of atoms thereof, which may equal zero and still fulfill the requirements of our invention, F represents fluorine and p the number of atoms thereof which is always equal to one or more.

X represents chlorine, bromine or iodine or combinations thereof and r the total number of such atoms. r may be zero when p is greater than one. v

Among the chemical groups that these refrigerants fall in are halogen derivatives of allphatic mono-fluorides, halogen derivatives of alkylv mono-fiuorides, aliphatic fluoro halides, alkyl iiuoro halides, fluoro derivatives of methyl lfluoride, luoro-halo derivatives of methane and fluoro chloro derivatives of methane.

Thus by our mode of making fiuorine and/or Aother halogen substitution in a mono-fluoride, We

\ changing the physical state of, for example, condensing or evaporating our aliphatic hydrocarbon derivative which contains more than one fluorine atom with or without other halogen atoms, or one uorine atom with one or more other halogen atoms, and by dissipating to or withdrawing from an object to be heated or cooled, the latent heat necessary for the change in physical state. More specifically, to produce refrigeration, we may evaporate the desired derivative in the vicinity of a body to be cooled, while if a heating effect is desired, we may condense the derivative in the vicinity of a body to be heated, it being understood, of course, that the terms evaporation and condensation include the separation of a gas from, and the absorption of a gas in, an absorbent respectively.

Our invention will probably nd its greatest utility by adjusting both the mode of preparing the refrigerant to obtain desirable characteristics and the mode of using the refrigerant to obtain a process of refrigeration or heat transfer which meets the limitations imposed. We prefer to employ refrigerants boiling above C.

Obviously our invention is not limited in its application to any specific form of apparatus for carrying out the mode of operation described and it will not be necessary for a complete understanding of the invention to show a specific embodiment of apparatus. Nor is the present invention limited to the examples set forth, for a particular advance of the present invention resides in the fact that a great number of new refrigerants with graduated properties is rendered available, and that one is accordingly enabled to secure the most suitable refrigerant for varied purposes.

W'hat is claimed is as follows:

1. The process of transferring heat which comprises condensing and subsequently evaporating CHaCClFz.

2. The process of transferring heat which comprises condensing and subsequently evaporating CHsCClzF.

3. The process of transferring heat which comprises condensing and subsequently evaporating a halo-fluoro derivative of ethan having the general formula CzHaXmF(3-m) where X equals a halogen other than fluorine and is neverless than one.

4. The process of transferring heat which comprises condensing and subsequently evaporating a halo-fluoro derivative of ethan having the general formula C2H3ClmF(3 m) where m is never less than one,

5. The process of transferring heat which comprises condensing and subsequently evaporating any halo-nuoro derivative of ethane having the general formula CzHnXmFs-(Mm) where X equals a halogen other than uorine and 11. and m are never less than one.

6. The process of producing refrigeration which comprises evaporating in the vicinity of a body to be cooled and subsequently condensing any halo-fluoro derivative of ethane having they 

